Modeling Near-Field Data at NTS and Amchitka

  1. Steven R. Taylor,
  2. Howard J. Patton and
  3. Paul G. Richards
  1. Don Helmberger,
  2. Larry Burdick and
  3. Richard Stead

Published Online: 18 MAR 2013

DOI: 10.1029/GM065p0035

Explosion Source Phenomenology

Explosion Source Phenomenology

How to Cite

Helmberger, D., Burdick, L. and Stead, R. (1991) Modeling Near-Field Data at NTS and Amchitka, in Explosion Source Phenomenology (eds S. R. Taylor, H. J. Patton and P. G. Richards), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM065p0035

Author Information

  1. Geological and Planetary Sciences, Seismological Laboratory, California Institute of Technology, pasadena, California 91125

Publication History

  1. Published Online: 18 MAR 2013
  2. Published Print: 1 JAN 1991

ISBN Information

Print ISBN: 9780875900315

Online ISBN: 9781118663820

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Keywords:

  • Underground nuclear explosions—Detection—Congresses;
  • Seismology—Congresses

Summary

The recent JVE (Joint Verification Experiment), involving shots of roughly the same yield at test sites in the US and USSR, showed an offset in teleseismic measured mfc. This is generally believed to be caused by differential attenuation beneath the two test sites. However, part of this difference could be caused by other factors such as variations in the effective source excitation or reduced displacement potential (RDP). In this review near-field seismograms from Amchitka and NTS are investigated to determine their source characteristics where the yields are known independently. To retrieve these RDP's requires separating out waveform distortions caused by complex local structures. After dealing with these crustal modeling problems we find distinct differences between these two test sites. Using a modified Haskell source representation given by we review estimates of k, B, and φ for both test sites required to model the P waveform data.

If we assume that B = 1 we find corner frequency (k) to be 20% smaller at Amchitka than at Pahute. This implies a larger effective source volume at Pahute for the same yield. The scaling of φ to yield indicates about 30% stronger coupling at Amchitka relative to Pahute. Assuming other source descriptions would not change these results appreciably in the frequency range (0.5 to 5 Hz). Allowing the overshoot factor B to vary and modeling broad-band information indicate that B for larger events (deep) tends to drop relative to small events (shallow). This effect is explained physically by allowing the explosion cavity to change shape, going from oblate (pancake) to prolate with increased depth. This phenomenon could have important implications considering that the Soviets tend to use a reduced depth-to-yield scale relative to that employed by the U.S.